Mobile communication systems have been developed because there has been a need to free people to move away from fixed telephone terminals without this hindering their reachability. While the use of different data transmission services in offices has increased, different data services have also been introduced into mobile communication systems. Portable computers enable efficient data processing everywhere the user moves. As for mobile communication networks, they provide the user with an efficient access network for mobile data transmission, such an access network providing access to actual data networks. In order to do this, different new data services are designed for existing and future mobile communication networks. Digital mobile communication systems, such as the pan-European mobile communication system GSM (Global System for Mobile Communication), support particularly well mobile data transmission.
General Packet Radio Service GPRS is a new service in the GSM system, and it is one the items of the standardization work of the GSM phase 2+ in ETSI (European Telecommunication Standard Institute). The GPRS operational environment consists of one or more sub-network service areas, which are interconnected by a GPRS backbone network. A sub-network comprises a number of packet data service nodes, which are referred to as GPRS support nodes (or agents) in this context, each packet data service node being connected to a GSM mobile communication network in such a manner that it is capable of providing a packet data service for mobile data terminal equipments via several base stations, i.e. cells. The intermediate mobile communication network provides circuit switched or packet switched data transmission between a support node and mobile data terminal equipments. Different sub-networks are connected to an external data network, such as a public switched packet data network PSPDN. The GPRS service thus produces packet data transmission between mobile data terminal equipments and external data networks, a GSM network acting as an access network. One aspect of the GPRS service network is that it operates almost independently of the GSM network. One of the requirements set for the GPRS service is that it must operate together with external PSPDNs of different types, for instance with Internet or X.25 networks. In other words, the GPRS service and a GSM network should be capable of serving all users, irrespective of which type of data networks they want to register in via the GSM network or which protocols are used in a data terminal equipment. This means that the GSM network and the GPRS service have to support and handle different network addressings and data packet formats, and be prepared for new (future) data network protocols.